A recent innovation in the production of decorative sheet type vinyl floor covering is the so-called "lay flat-stay flat" flooring. Presently available flooring of this type contains an inner web of staple glass fibers bonded with a thermoset resin, usually a urea-formaldehyde resin. This glass fiber web is coated on both sides, e.g., with a filled polyvinyl chloride plastisol, before additional layers are applied to produce a floor covering material. This flooring material is superior in flatness to conventional vinyl floor coverings produced by one side coating of backing felts.
Flooring products containing these thermoset resin-impregnated glass fiber inner webs have a tendency to buckle, especially when installed over certain substrates such as wood flooring. Wood flooring changes in dimensions with changes in relative humidity, and the flooring material containing the thermoset resin-impregnated glass fiber inner web is too stiff to move with the substrate. A more flexible floor covering capable of changing dimensions at the same rate as the substrate to which it is applied would not have such a tendency to buckle.